1. Field of the Invention
The present invention relates to an image-forming apparatus, such as an electro-photographic printer or a copier, in which an electro-static latent image on an image carrying body is reproduced by a toner. More specifically, it relates to a system for controlling a drive of a toner agitator in such an image-forming apparatus at an initial stage of the operation thereof.
2. Description of the Related Art
As illustrated in FIGS. 1 through 4, an electro-photograph printer 1 comprises lower and upper frames 1a, 1b, and a process cartridge 2, transfer-charger 3, and fuser unit 4 mounted therein. The process cartridge 2 consists of a photoconductive drum 5 around which a developer unit 8, a precharger 7, and a cleaner 9 are arranged; all of these elements being built-in to a case 2a and forming a cartridge. A main motor M is provided in the lower frame 1a for driving the photoconductive drum 5, the fuser unit 4, and a plurality of rollers 6a, 6b for advancing a sheet 25. As shown in FIGS. 2 and 4, the process cartridge 2 is inserted into or removed from the interior of the printer 1 through an opening 17 formed between the lower and upper frames 1a and 1b when the upper frame 1b is separated from the lower frame 1a by a pivoting motion of the upper frame 1b about a pin 14.
In the printing operation, cut sheets 25 are fed one by one from a hopper 10a or 10b and transported by a plurality of rollers 6a, 6b into an area between the transfer-charger 3 and the photoconductive drum 5, then past the fuser unit 4 and are discharged on a stacker 12.
As shown in FIG. 5, the precharger 7, an LED-array 11, the developer unit 8, the transfer-charger 3, and the cleaner 9 are sequentially arranged around the photoconductive drum 5, and accordingly, during a counter-clockwise rotation of the drum 5, the periphery thereof is uniformly charged by the precharger 7. Then the electro-static latent image is formed on the drum periphery by the LED-array 11 in accordance with information input and is reproduced as a toner image by the developer unit 8. Thereafter, the toner image is transferred to the surface of the cut sheet 25 by the transfer-charger 3 and fixed thereon by the fuser unit 4, and finally, the cut sheet 25 is discharged as a hard copy onto the stacker 12.
In this connection, the developer unit 8 accommodates an agitator 13 therein for stirring a powdery toner 15 filled in the unit 8 and delivering the same to a magnet roller 14, as shown in FIG. 5. The agitator 13 is also driven by the main motor M. In the conventional printer, the motor M is rotated at substantially the same speed at the warming-up stage of the printer as during a normal printing operation.
The powdery toner 15 filled in the developer unit 8 is liable to solidify when the process cartridge 2 is stored on a shelf for a long time, for example, more than one week or one month, or suffers from a vibration during transportation, whereby the apparent density thereof is increased from 30% to 40%. If the process cartridge 2 in which the toner is solidified is initially set on the printer, the agitator 13 is subjected to a larger rotational load at the warming-up stage of the operation, and this may cause damage to or deformation of the agitator 13.
In general, an initialization is carried out at the beginning of the printing operation to ensure a better printing quality. The initialization is made by energizing the elements of the printer for a short period, to initialize the printer conditions. The steps of the initialization process are sequentially checked by a control unit corresponding to the predetermined time schedule starting simultaneously with the switch-on of the motor. As stated before, if the toner has solidified, the rotation of the main motor M, which is substantially the only drive source for the rotating elements of the printer, is obstructed thereby at the beginning of rotation. Accordingly, the initialization schedule is delayed and an error signal is generated from the control unit.
The above drawbacks can be eliminated by the provision of a larger capacity motor which can overcome the resistance from the solidified toner, but such a larger motor is uneconomical, since the solidified toner can be restored to the required state by only one rotation of the agitator.